Solid electrolyte material and battery using same

ABSTRACT

The solid electrolyte material of the present disclosure is a solid electrolyte material made of Li, Ca, Y, Gd, X, and O, where X is at least one selected from the group consisting of F, Cl, Br, and I; the molar ratio of O to the sum of Y and Gd in the entire solid electrolyte material is greater than 0 and 0.42 or less; and O is present in a surface region of the solid electrolyte material.

BACKGROUND 1. Technical Field

The present disclosure relates to a solid electrolyte material and abattery using it.

2. Description of the Related Art

Japanese Unexamined Patent Application Publication No. 2011-129312discloses an all solid state battery using a sulfide solid electrolyte.International Publication No. WO 2018/025582 discloses a solidelectrolyte material represented by Li_(6−3z)Y_(z)X₆ (0<z<2 issatisfied, and X is Cl or Br).

SUMMARY

One non-limiting and exemplary embodiment provides a solid electrolytematerial having a high lithium ion conductivity.

In one general aspect, the techniques disclosed here feature a solidelectrolyte material made of Li, Ca, Y, Gd, X, and O, where X is atleast one selected from the group consisting of F, Cl, Br, and I; themolar ratio of O to the sum of Y and Gd in the entire solid electrolytematerial is greater than 0 and 0.42 or less; and the molar ratio of O tothe sum of Y and Gd in a surface region of the solid electrolytematerial is higher than the molar ratio of O to the sum of Y and Gd inthe entire solid electrolyte material.

The present disclosure provides a solid electrolyte material having ahigh lithium ion conductivity.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a cross-sectional view of a battery according to a secondembodiment;

FIG. 2 is a graph showing X-ray diffraction patterns of solidelectrolyte materials of Examples 1 to 4 and Comparative Example 1;

FIG. 3 is a schematic view of a compression molding die used forevaluation of the ion conductivity of a solid electrolyte material;

FIG. 4 is a graph showing a Cole-Cole chart of the impedance measurementresults of the solid electrolyte material of Example 1; and

FIG. 5 is a graph showing the initial discharge characteristics of thebatteries of Example 1 and Comparative Example 1.

DETAILED DESCRIPTIONS

Embodiments of the present disclosure will now be described withreference to the drawings.

First Embodiment

The solid electrolyte material according to a first embodiment is madeof Li, Ca, Y, Gd, X, and O. Here, X is at least one selected from thegroup consisting of F, Cl, Br, and I; the molar ratio of O to the sum ofY and Gd in the entire solid electrolyte material according to the firstembodiment is greater than 0 and 0.42 or less; and the molar ratio of Oto the sum of Y and Gd in a surface region of the solid electrolytematerial is higher than the molar ratio of O to the sum of Y and Gd inthe entire solid electrolyte material.

Here, the surface region of the solid electrolyte material according tothe first embodiment means the region of the solid electrolyte materialfrom the surface to a depth of about 5 nm in the inward direction.

The solid electrolyte material according to the first embodiment has ahigh lithium ion conductivity. Here, the high lithium ion conductivityis, for example, 1×10⁻⁵ S/cm or more. That is, the solid electrolytematerial according to the first embodiment can have, for example, an ionconductivity of 1×10⁻⁵ S/cm or more.

The solid electrolyte material according to the first embodiment can beused for obtaining an all solid state battery having excellent chargeand discharge characteristics. The all solid state battery may be aprimary battery or a secondary battery.

The solid electrolyte material according to the first embodimentdesirably does not contain sulfur. A solid electrolyte material notcontaining sulfur does not generate hydrogen sulfide, even if it isexposed to the atmosphere, and is therefore excellent in safety. Thesulfide solid electrolyte disclosed in Japanese Unexamined PatentApplication Publication No. 2011-129312 may generate hydrogen sulfidewhen it is exposed to the atmosphere.

The solid electrolyte material according to the first embodiment mayconsist essentially of Li, Ca, Y, Gd, X, and O. The phrase “the solidelectrolyte material according to the first embodiment consistsessentially of Li, Ca, Y, Gd, X, and O” means that the molar proportion(i.e., molar fraction) of the sum of the amounts of Li, Ca, Y, Gd, X,and O to the sum of the amounts of all elements constituting the solidelectrolyte material in the solid electrolyte material according to thefirst embodiment is 90% or more. As an example, the molar proportion maybe 95% or more. The solid electrolyte material according to the firstembodiment may consist of Li, Ca, Y, Gd, X, and O only.

In order to enhance the ion conductivity of the solid electrolytematerial, X may be Cl and Br.

In order to enhance the ion conductivity of the solid electrolytematerial, the solid electrolyte material according to the firstembodiment may further include at least one selected from the groupconsisting of Sr, Ba, Al, Sc, Ga, Bi, La, Zr, Hf, Ta, and Nb.

The transition metal included in the solid electrolyte materialaccording to the present embodiment may be only Y and Gd excludingelements included as inevitable impurities.

The molar ratio “A” of O to the sum of Y and Gd in the surface region ofthe solid electrolyte material according to the first embodiment may begreater than the molar ratio “B” of O to the sum of Y and Gd in theentire solid electrolyte material. Such a solid electrolyte material hasa high ion conductivity. As an example, the value of the molar ratio “A”may be five or more times the value of the molar ratio “B”.

In order for the solid electrolyte material to have a high ionconductivity, the molar ratio “A” of the solid electrolyte materialaccording to the first embodiment may be 0.50 or more and 2.75 or less.

In order for the solid electrolyte material to have a high ionconductivity, the upper limit and the lower limit of the range of themolar ratio “A” of the solid electrolyte material according to the firstembodiment may be defined by an arbitrary combination selected from thenumerical values of 2.08, 2.38, 2.47, 2.68, and 2.75.

The X-ray diffraction pattern of the solid electrolyte materialaccording to the first embodiment can be obtained using Cu-Kα rays. Inthe obtained X-ray diffraction pattern, peaks may be present indiffraction angle 2θ ranges of 14.9° or more and 16.10 or less, 16.2° ormore and 17.5° or less, 22.3° or more and 23.6° or less, 29.9° or moreand 31.2° or less, and 32.10 or more and 33.5° or less. Such a solidelectrolyte material has a high ion conductivity.

In order to enhance the ion conductivity of the solid electrolytematerial, the following four mathematical expressions may be satisfied:

2.5≤x≤3.2;

0.06≤y≤0.08;

0.9≤z≤1.9; and

2.4≤w≤4.4,

wherein

x represents a molar ratio of Li to the sum of Y and Gd;

y represents a molar ratio of Ca to the sum of Y and Gd;

z represents a molar ratio of Br to the sum of Y and Gd; and

w represents a molar ratio of Cl to the sum of Y and Gd.

In order to further enhance the ion conductivity of the solidelectrolyte material, the following four mathematical expressions may besatisfied:

2.8≤x≤2.9;

0.06≤y≤0.08;

1.0≤z≤1.8; and

2.6≤w≤4.0.

In order to enhance the ion conductivity of the solid electrolytematerial, the molar ratio of O to the sum of Y and Gd in the entiresolid electrolyte material according to the first embodiment may begreater than 0 and 0.2 or less. The molar ratio of O to the sum of Y andGd in the entire solid electrolyte material may be greater than 0 and0.09 or less. The molar ratio of O to the sum of Y and Gd in the entiresolid electrolyte material may be greater than 0 and 0.08 or less.

The shape of the solid electrolyte material according to the firstembodiment is not limited. Examples of the shape are needle, spherical,and oval spherical shapes. The solid electrolyte material according tothe first embodiment may be a particle. The solid electrolyte materialaccording to the first embodiment may be formed so as to have a pelletor planar shape.

When the shape of the solid electrolyte material according to the firstembodiment is a particulate shape (e.g., spherical), the solidelectrolyte material according to the first embodiment may have a mediandiameter of 0.1 μm or more and 100 μm or less.

In order to enhance the ion conductivity of the solid electrolytematerial according to the first embodiment and to well disperse thesolid electrolyte material according to the first embodiment and anactive material, the median diameter may be 0.5 μm or more and 10 μm orless. In order to better disperse the solid electrolyte materialaccording to the first embodiment and the active material, the solidelectrolyte material according to the first embodiment may have a mediandiameter smaller than that of the active material. The median diametermeans the particle diameter at which the accumulated volume in avolume-based particle size distribution is equal to 50%. Thevolume-based particle size distribution can be measured with a laserdiffraction measurement apparatus or an image analyzer.

Method for Manufacturing Solid Electrolyte Material

The solid electrolyte material according to the first embodiment can bemanufactured by the following method.

First, a plurality of halides as raw material powders are mixed.

As an example, when a solid electrolyte material consisting of Li, Ca,Y, Gd, Br, Cl, and O is produced, a LiCl raw material powder, a LiBr rawmaterial powder, a YCl₃ raw material powder, a GdCl₃ raw materialpowder, and CaBr₂ are mixed. The resulting powder mixture isheat-treated in an inert gas atmosphere with adjusted oxygenconcentration and moisture concentration (for example, an argonatmosphere having a dew point of −60° C. or less). The heat treatmenttemperature may be, for example, within a range of 200° C. or more and650° C. or less. The resulting heat treatment product is left to standin an atmosphere having a relatively high dew point (for example, a dryatmosphere having a dew point of −30° C.).

Subsequently, heat treatment is performed, for example, in an inert gasatmosphere with adjusted oxygen concentration and moisture concentration(for example, an argon atmosphere having a dew point of −60° C. or less)at a temperature of the melting point or less (for example, 400° C.).The proportion of O in the surface region of the solid electrolytematerial is increased by the heat treatment at a temperature lower thanthe melting point. The raw material powders may be mixed at a molarratio adjusted in advance so as to offset a composition change that mayoccur in the synthesis process. The oxygen amount in a solid electrolytematerial is determined by selecting the raw material powders, the oxygenconcentration in the atmosphere, the moisture concentration in theatmosphere, and the reaction time. Thus, the solid electrolyte materialaccording to the first embodiment is obtained.

The raw material powders to be mixed may be an oxide and a halide. Forexample, as the raw material powders, Y₂O₃, Gd₂O₃, NII₄Cl, NH₄Br, LiCl,LiBr, and CaBr₂ may be used.

It is inferred that the oxygen constituting the solid electrolytematerial according to the first embodiment is incorporated from theabove-mentioned atmosphere having a relatively high dew point.

Second Embodiment

A second embodiment will now be described. The matters described in thefirst embodiment may be omitted.

The battery according to the second embodiment includes a positiveelectrode, a negative electrode, and an electrolyte layer. Theelectrolyte layer is disposed between the positive electrode and thenegative electrode. At least one selected from the group consisting ofthe positive electrode, the electrolyte layer, and the negativeelectrode contains the solid electrolyte material according to the firstembodiment. The battery according to the second embodiment contains thesolid electrolyte material according to the first embodiment andtherefore has excellent charge and discharge characteristics. Thebattery may be an all solid state battery.

FIG. 1 shows a cross-sectional view of a battery 1000 according to thesecond embodiment.

The battery 1000 includes a positive electrode 201, an electrolyte layer202, and a negative electrode 203. The electrolyte layer 202 is disposedbetween the positive electrode 201 and the negative electrode 203.

The positive electrode 201 contains a positive electrode active materialparticle 204 and a solid electrolyte particle 100.

The electrolyte layer 202 contains an electrolyte material (for example,a solid electrolyte material).

The negative electrode 203 contains a negative electrode active materialparticle 205 and a solid electrolyte particle 100.

The solid electrolyte particle 100 is a particle consisting of the solidelectrolyte material according to the first embodiment or a particlecontaining the solid electrolyte material according to the firstembodiment as a main component. Here, the particle containing the solidelectrolyte material according to the first embodiment as a maincomponent means a particle in which the most abundant component in termsof mass proportion is the solid electrolyte material according to thefirst embodiment.

The positive electrode 201 contains a material that can occlude andrelease metal ions (for example, lithium ions). The material is, forexample, a positive electrode active material (for example, the positiveelectrode active material particle 204).

Examples of the positive electrode active material are alithium-containing transition metal oxide, a transition metal fluoride,a polyanionic material, a fluorinated polyanionic material, a transitionmetal sulfide, a transition metal oxyfluoride, a transition metaloxysulfide, and a transition metal oxynitride. Examples of thelithium-containing transition metal oxide are LiNi_(1−d−f)Co_(d)Al_(f)O₂(here, 0<d, 0<f, and 0<(d+f)<1) and LiCoO₂.

In order to well disperse the positive electrode active materialparticle 204 and the solid electrolyte particle 100 in the positiveelectrode 201, the positive electrode active material particle 204 mayhave a median diameter of 0.1 μm or more. This good dispersion improvesthe charge and discharge characteristics of the battery 1000. In orderto rapidly diffuse lithium in the positive electrode active materialparticle 204, the positive electrode active material particle 204 mayhave a median diameter of 100 μm or less. The battery 1000 can beoperated at a high output due to the rapid diffusion of lithium. Asdescribed above, the positive electrode active material particle 204 mayhave a median diameter of 0.1 μm or more and 100 μm or less.

In order to well disperse the positive electrode active materialparticle 204 and the solid electrolyte particle 100 in the positiveelectrode 201, the positive electrode active material particle 204 mayhave a median diameter larger than that of the solid electrolyteparticle 100.

In order to increase the energy density and output of the battery 1000,in the positive electrode 201, the ratio of the volume of the positiveelectrode active material particle 204 to the sum of the volume of thepositive electrode active material particle 204 and the volume of thesolid electrolyte particle 100 may be 0.30 or more and 0.95 or less.

In order to increase the energy density and output of the battery 1000,the positive electrode 201 may have a thickness of 10 μm or more and 500μm or less.

The electrolyte layer 202 contains an electrolyte material. Theelectrolyte material may be the solid electrolyte material according tothe first embodiment. The electrolyte layer 202 may be a solidelectrolyte layer.

The electrolyte layer 202 may be constituted of only the solidelectrolyte material according to the first embodiment. Alternatively,the electrolyte layer 202 may be constituted of only a solid electrolytematerial that is different from the solid electrolyte material accordingto the first embodiment.

Examples of the solid electrolyte material that is different from thesolid electrolyte material according to the first embodiment areLi₂MgX′₄, Li₂FeX′₄, Li(Al,Ga,In)X′₄, Li₃(Al,Ga,In)X′₆, and LiI. Here, Xis at least one selected from the group consisting of F, Cl, Br, and I.

In the present disclosure, “(A,B,C)” means “at least one selected fromthe group consisting of A, B, and C”.

Hereinafter, the solid electrolyte material according to the firstembodiment is called a first solid electrolyte material. The solidelectrolyte material that is different from the solid electrolytematerial according to the first embodiment is called a second solidelectrolyte material.

The electrolyte layer 202 may contain not only the first solidelectrolyte material but also the second solid electrolyte material. Thefirst solid electrolyte material and the second solid electrolytematerial may be uniformly dispersed. A layer made of the first solidelectrolyte material and a layer made of the second solid electrolytematerial may be stacked along the stacking direction of the battery1000.

In order to prevent short circuit between the positive electrode 201 andthe negative electrode 203 and to increase the output of the battery1000, the electrolyte layer 202 may have a thickness of 1 μm or more and100 μm or less.

The negative electrode 203 contains a material that can occlude andrelease metal ions (for example, lithium ions). The material is, forexample, a negative electrode active material (for example, the negativeelectrode active material particle 205).

Examples of the negative electrode active material are a metal material,a carbon material, an oxide, a nitride, a tin compound, and a siliconcompound. The metal material may be a single metal or an alloy. Examplesof the metal material are a lithium metal and a lithium alloy. Examplesof the carbon material are natural graphite, coke, graphitizing carbon,carbon fibers, spherical carbon, artificial graphite, and amorphouscarbon. From the viewpoint of capacity density, suitable examples of thenegative electrode active material are silicon (i.e., Si), tin (i.e.,Sn), a silicon compound, and a tin compound.

In order to well disperse the negative electrode active materialparticle 205 and the solid electrolyte particle 100 in the negativeelectrode 203, the negative electrode active material particle 205 mayhave a median diameter of 0.1 μm or more. The good dispersion improvesthe charge and discharge characteristics of the battery. In order torapidly disperse lithium in the negative electrode active materialparticle 205, the negative electrode active material particle 205 mayhave a median diameter of 100 μm or less. The battery can be operated ata high output due to the rapid diffusion of lithium. As described above,the negative electrode active material particle 205 may have a mediandiameter of 0.1 μm or more and 100 μm or less.

In order to well disperse the negative electrode active materialparticle 205 and the solid electrolyte particle 100 in the negativeelectrode 203, the negative electrode active material particle 205 mayhave a median diameter larger than that of the solid electrolyteparticle 100.

In order to increase the energy density and output of the battery 1000,in the negative electrode 203, the ratio of the volume of the negativeelectrode active material particle 205 to the sum of the volume of thenegative electrode active material particle 205 and the volume of thesolid electrolyte particle 100 may be 0.30 or more and 0.95 or less.

In order to increase the energy density and output of the battery 1000,the negative electrode 203 may have a thickness of 10 μm or more and 500μm or less.

In order to enhance the ion conductivity, chemical stability, andelectrochemical stability, at least one selected from the groupconsisting of the positive electrode 201, the electrolyte layer 202, andthe negative electrode 203 may contain the second solid electrolytematerial.

As described above, the second solid electrolyte material may be ahalide solid electrolyte. Examples of the halide solid electrolyte areLi₂MgX′₄, Li₂FeX′₄, Li(Al,Ga,In)X′₄, Li₃(Al,Ga,In)X′₆, and LiI. Here, Xis at least one selected from the group consisting of F, Cl, Br, and I.

The second solid electrolyte material may be a sulfide solidelectrolyte.

Examples of the sulfide solid electrolyte are Li₂S—P₂S₅, Li₂S—SiS₂,Li₂S—B₂S₃, Li₂S—GeS₂, Li_(3.25)Ge_(0.25)P_(0.75)S₄, and Li₁₀GeP₂Si₂.

The second solid electrolyte material may be an oxide solid electrolyte.

Examples of the oxide solid electrolyte are:

(i) an NASICON-type solid electrolyte, such as LiTi₂(PO₄)₃ or itselement substitute;

(ii) a perovskite-type solid electrolyte, such as (LaLi)TiO₃;

(iii) an LISICON-type solid electrolyte, such as Li₁₄ZnGe₄O₁₆, Li₄SiO₄,LiGeO₄, or its element substitute;

(iv) a garnet-type solid electrolyte, such as Li₇La₃Zr₂O₁₂ or itselement substitute; and

(v) Li₃PO₄ or its N-substitute.

The second solid electrolyte material may be an organic polymer solidelectrolyte.

Examples of the organic polymer solid electrolyte are a polymer compoundand a compound of a lithium salt. The polymer compound may have anethylene oxide structure.

A polymer compound having an ethylene oxide structure can contain alarge amount of a lithium salt and can therefore further enhance the ionconductivity.

Examples of the lithium salt are LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiSO₃CF₃,LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉), and LiC(SO₂CF₃)₃. Onelithium salt selected from these salts may be used alone. Alternatively,a mixture of two or more lithium salts selected from these salts may beused.

At least one selected from the group consisting of the positiveelectrode 201, the electrolyte layer 202, and the negative electrode 203may contain a nonaqueous electrolyte liquid, a gel electrolyte, or anionic liquid for the purpose of facilitating the transfer of lithiumions and improving the output characteristics of the battery 1000.

The nonaqueous electrolyte liquid contains a nonaqueous solvent and alithium salt dissolved in the nonaqueous solvent.

Examples of the nonaqueous solvent are a cyclic carbonate ester solvent,a chain carbonate ester solvent, a cyclic ether solvent, a chain ethersolvent, a cyclic ester solvent, a chain ester solvent, and a fluorinesolvent. Examples of the cyclic carbonate ester solvent are ethylenecarbonate, propylene carbonate, and butylene carbonate. Examples of thechain carbonate ester solvent are dimethyl carbonate, ethyl methylcarbonate, and diethyl carbonate. Examples of the cyclic ether solventare tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of thechain ether solvent are 1,2-dimethoxyethane and 1,2-diethoxyethane. Anexample of the cyclic ester solvent is γ-butyrolactone. An example ofthe chain ester solvent is methyl acetate. Examples of the fluorinesolvent are fluoroethylene carbonate, methyl fluoropropionate,fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylenecarbonate. One nonaqueous solvent selected from these solvents may beused alone. Alternatively, a mixture of two or more nonaqueous solventsselected from these solvents may be used.

Examples of the lithium salt are LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiSO₃CF₃,LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉), and LiC(SO₂CF₃)₃. Onelithium salt selected from these salts may be used alone. Alternatively,a mixture of two or more lithium salts selected from these salts may beused.

The concentration of the lithium salt is, for example, within a range of0.5 mol/L or more and 2 mol/L or less.

As the gel electrolyte, a polymer material impregnated with a nonaqueouselectrolyte liquid can be used. Examples of the polymer material arepolyethylene oxide, polyacrylonitrile, polyvinylidene fluoride,polymethyl methacrylate, and a polymer having an ethylene oxide bond.

Examples of the cation included in the ionic liquid are:

(i) an aliphatic chain quaternary salt, such as tetraalkylammonium andtetraalkylphosphonium;

(ii) an alicyclic ammonium, such as pyrrolidiniums, morpholiniums,imidazoliniums, tetrahydropyrimidiniums, piperaziniums, andpiperidiniums; and

(iii) a nitrogen-containing heterocyclic aromatic cation, such aspyridiniums and imidazoliums.

Examples of the anion included in the ionic liquid are PF₆ ⁻, BF₄ ⁻,SbF₆ ⁻, AsF⁻, SO₃CF₃ ⁻, N(SO₂CF₃)₂ ⁻, N(SO₂C₂F₅)₂, N(SO₂CF₃)(SO₂C₄F₉)⁻,and C(SO₂CF₃)₃ ⁻.

The ionic liquid may contain a lithium salt.

At least one selected from the group consisting of the positiveelectrode 201, the electrolyte layer 202, and the negative electrode 203may contain a binder for the purpose of improving the adhesion betweenindividual particles.

Examples of the binder are polyvinylidene fluoride,polytetrafluoroethylene, polyethylene, polypropylene, an aramid resin,polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylicacid, polyacrylic acid methyl ester, polyacrylic acid ethyl ester,polyacrylic acid hexyl ester, polymethacrylic acid, polymethacrylic acidmethyl ester, polymethacrylic acid ethyl ester, polymethacrylic acidhexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether,polyether sulfone, hexafluoropolypropylene, styrene butadiene rubber,and carboxymethyl cellulose.

A copolymer can also be used as the binder. Examples of such the binderare copolymers of two or more materials selected from the groupconsisting of tetrafluoroethylene, hexafluoroethylene,hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride,chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene,fluoromethyl vinyl ether, acrylic acid, and hexadiene. A mixture of twoor more selected from these materials may be used as the binder.

At least one selected from the positive electrode 201 and the negativeelectrode 203 may contain a conductive assistant for the purpose ofenhancing the electron conductivity.

Examples of the conductive assistant are:

(i) graphites, such as natural graphite and artificial graphite;

(ii) carbon blacks, such as acetylene black and Ketjen black;

(iii) conductive fibers, such as carbon fibers and metal fibers;

(iv) carbon fluoride;

(v) metal powders, such as aluminum;

(vi) conductive whiskers, such as zinc oxide and potassium titanate;

(vii) a conductive metal oxide, such as titanium oxide; and

(viii) a conductive polymer compound, such as polyaniline, polypyrrole,and polythiophene. In order to reduce the cost, the conductive assistantof the above (i) or (ii) may be used.

Examples of the shape of the battery according to the second embodimentare coin type, cylindrical type, square type, sheet type, button type,flat type, and stack type.

The battery according to the second embodiment may be manufactured by,for example, providing a material for forming a positive electrode, amaterial for forming an electrolyte layer, and a material for forming anegative electrode and producing a stack of a positive electrode, anelectrolyte layer, and a negative electrode disposed in this order by aknown method.

EXAMPLES

The present disclosure will now be described in more detail withreference to Examples.

Example 1 Production of Solid Electrolyte Material

LiCl, LiBr, YCl₃, GdCl₃, and CaBr₂ were provided as raw material powderssuch that the LiCl:LiBr:YCl₃:GdCl₃:CaBr₂ molar ratio was1:1.85:0.5:0.5:0.075 in an argon atmosphere having a dew point of −60°C. or less and an oxygen concentration of 0.0001 vol % or less(hereinafter, referred to as “dry argon atmosphere”). These raw materialpowders were pulverized and mixed in a mortar. The resulting mixture washeat-treated in an alumina crucible at 500° C. for 1 hour and was thenpulverized in a mortar. The resulting heat treatment product was left tostand in a dry atmosphere having a dew point of −30° C. and an oxygenconcentration of 20.9 vol % or less for about 30 minutes. The heattreatment product was further heat-treated in the dry argon atmosphereat 400° C. for 1 hour and then pulverized in a mortar. Thus, a solidelectrolyte material of Example 1 was obtained.

Composition Analysis of Solid Electrolyte Material

The contents of Li, Ca, Y, and Gd per unit weight of the solidelectrolyte material of Example 1 were measured with a high-frequencyinductively coupled plasma emission spectrometer (manufactured by ThermoFisher Scientific, Inc., iCAP7400) by high-frequency inductively coupledplasma emission spectrometry. The contents of Cl and Br in the solidelectrolyte material of Example 1 were measured with an ionchromatography apparatus (manufactured by Dionex, ICS-2000) by an ionchromatography method. The Li:Ca:Y:Gd:Br:Cl molar ratio was calculatedbased on the contents of Li, Ca, Y, Gd, Br, and Cl obtained from thesemeasurements. As a result, the solid electrolyte material of Example 1had a Li:Ca:Y:Gd:Br:Cl molar ratio of 2.88:0.07:0.50:0.50:1.70:3.97.

The mass proportion of O to the entire solid electrolyte material ofExample 1 was measured with an oxygen nitrogen hydrogen analyzer(manufactured by HORIBA, Ltd., EMGA-930) by a nondispersive infraredabsorption method. As a result, the mass proportion of O was 0.28%.Based on this, the (Y+Gd):O molar ratio was calculated. As a result, thesolid electrolyte material of Example 1 had a (Y+Gd):O molar ratio of1.00:0.08.

The molar ratio of O to the sum of Y and Gd in a surface region of thesolid electrolyte material of Example 1 was measured with a scanningX-ray photoelectron spectrometer (manufactured by Ulvac-Phi, Inc., PHIQuantera SXM) by an X-ray photoelectron spectroscopy. As the X-raysource, Al-Kα rays were used. As a result, the solid electrolytematerial of Example 1 had a (Y+Gd):O molar ratio of 1.00:2.08 in thesurface region. The surface region in the present disclosure means thethus-measured region. The thickness of the surface region of the solidelectrolyte material according to the first embodiment was about 5 nmfrom the surface of the solid electrolyte material in the inwarddirection.

In the composition analysis, an element of which the molar fractionrelative to the sum of Y and Gd was 0.01% or less was recognized as animpurity.

X-ray Diffraction

The crystal structure of the solid electrolyte material was analyzedwith an X-ray diffractometer (RIGAKU Corporation, MiniFlex 600). TheX-ray diffraction pattern of the solid electrolyte material of Example 1was measured in a dry environment having a dew point of −45° C. or less.As the X-ray source, Cu-Kα rays (wavelength: 1.5405 angstrom and 1.5444angstrom) were used.

As the results of the X-ray diffraction measurement, there were peaks at15.42°, 16.80°, 22.86°, 27.70°, 28.72°, 30.54°, 32.74°, 39.76°, and47.50°. FIG. 2 is a graph showing an X-ray diffraction pattern of thesolid electrolyte material of Example 1.

Evaluation of Ion Conductivity

FIG. 3 is a schematic view of a compression molding die 300 used forevaluation of the ion conductivity of a solid electrolyte material.

The compression molding die 300 included a punch upper part 301, a framemold 302, and a punch lower part 303. The frame mold 302 was made ofinsulating polycarbonate. The punch upper part 301 and the punch lowerpart 303 were both made of electron-conductive stainless steel.

The ion conductivity of the solid electrolyte material of Example 1 wasmeasured using the compression molding die 300 shown in FIG. 3 by thefollowing method.

A powder 101 of the solid electrolyte material of Example 1 was loadedin the compression molding die 300 in the dry argon atmosphere. Apressure of 400 MPa was applied to the solid electrolyte material ofExample 1 inside the compression molding die 300 using the punch upperpart 301 and the punch lower part 303.

While applying the pressure, the punch upper part 301 and the punchlower part 303 were connected to a potentiostat (Princeton AppliedResearch, VersaSTAT4). The punch upper part 301 was connected to theworking electrode and the potential measurement terminal. The punchlower part 303 was connected to the counter electrode and the referenceelectrode. The impedance of the solid electrolyte material of Example 1was measured by an electrochemical impedance measurement method at roomtemperature.

FIG. 4 is a graph showing a Cole-Cole chart of the impedance measurementresults of the solid electrolyte material of Example 1.

In FIG. 4 , the real value of impedance at the measurement point wherethe absolute value of the phase of the complex impedance was thesmallest was regarded as the resistance value of the solid electrolytematerial to ion conduction. Regarding the real value, see the arrowR_(SE) shown in FIG. 4 . The ion conductivity was calculated using theresistance value based on the following mathematical expression (1):

σ=(R _(SE) ×S/t)⁻¹  (1).

Here, a represents ion conductivity; S represents the contact area of asolid electrolyte material with the punch upper part 301 (equal to thecross-sectional area of the hollow part of the frame mold 302 in FIG. 3); R_(SE) represents the resistance value of the solid electrolytematerial in impedance measurement; and t represents the thickness of thesolid electrolyte material applied with a pressure (equal to thethickness of the layer formed from the powder 101 of the solidelectrolyte material in FIG. 3 ).

The ion conductivity of the solid electrolyte material of Example 1measured at 25° C. was 1.2×10⁻³ S/cm.

Production of Battery

The solid electrolyte material of Example 1 and LiCoO₂ as an activematerial were provided at a volume ratio of 70:30 in the dry argonatmosphere. These materials were mixed in an agate mortar. Thus, amixture was obtained.

The solid electrolyte material (100 mg) of Example 1, the above mixture(10.0 mg), and an aluminum powder (14.7 mg) were stacked in this orderin an insulating tube having an inner diameter of 9.5 mm. A pressure of300 MPa was applied to this stack to form a first electrode and a solidelectrolyte layer. The solid electrolyte layer had a thickness of 500μm.

Subsequently, metal In foil was stacked on the solid electrolyte layer.The solid electrolyte layer was sandwiched between the metal In foil andthe first electrode. The metal In foil had a thickness of 200 μm.Subsequently, a pressure of 80 MPa was applied to the metal In foil toform a second electrode.

A current collector made of stainless steel was attached to the firstelectrode and the second electrode, and current collecting lead was thenattached to the current collector. Finally, the inside of the insulatingtube was isolated from the outside atmosphere using an insulatingferrule to seal the inside of the tube. Thus, a battery of Example 1 wasobtained.

Charge and Discharge Test

FIG. 5 is a graph showing the initial discharge characteristics of thebattery of Example 1. The results shown in FIG. 5 were measured by thefollowing method.

The battery of Example 1 was placed in a thermostatic chamber of 25° C.The battery of Example 1 was charged with a current density of 83 μA/cm²until the voltage reached 3.7 V. The current density corresponds to 0.05C rate. Subsequently, the battery of Example 1 was discharged similarlyat a current density of 83 μA/cm² until the voltage reached 1.9 V.

As the results of the charge and discharge test, the battery of Example1 had an initial discharge capacity of 552 μAh.

Examples 2 to 4

In Example 2, a solid electrolyte material of Example 2 was obtained asin Example 1 except that the time during which the heat treatmentproduct was left to stand in a dry atmosphere having a dew point of −30°C. and an oxygen concentration of 20.9 vol % or less was set to 1 hourinstead of about 30 minutes.

In Example 3, a solid electrolyte material of Example 3 was obtained asin Example 1 except that the time during which the heat treatmentproduct was left to stand in a dry atmosphere having a dew point of −30°C. and an oxygen concentration of 20.9 vol % or less was set to 15 hoursinstead of about 30 minutes.

In Example 4, a solid electrolyte material of Example 4 was obtained asin Example 1 except that the time during which the heat treatmentproduct was left to stand in a dry atmosphere having a dew point of −30°C. and an oxygen concentration of 20.9 vol % or less was set to 40 hoursinstead of about 30 minutes.

The element ratio (molar ratio), X-ray diffraction, and ion conductivityof each of the solid electrolyte materials of Examples 2 to 4 weremeasured as in Example 1. The measurement results are shown in Tables 1and 2. FIG. 2 is a graph showing X-ray diffraction patterns of the solidelectrolyte materials of Examples 2 to 4.

The mass proportions of O to the respective entire solid electrolytematerials of Examples 2 to 4 were 0.33%, 0.84%, and 1.82%.

Batteries of Examples 2 to 4 were obtained as in Example 1 using thesolid electrolyte materials of Examples 2 to 4.

A charge and discharge test was implemented as in Example 1 using thebatteries of Examples 2 to 4. The batteries of Examples 2 to 4 were wellcharged and discharged as in the battery of Example 1.

Comparative Example 1

In Comparative Example 1, a solid electrolyte material of ComparativeExample 1 was obtained as in Example 1 except that the time during whichthe heat treatment product was left to stand in a dry atmosphere havinga dew point of −30° C. and an oxygen concentration of 20.9 vol % or lesswas set to 80 hours instead of about 30 minutes.

The element ratio (molar ratio), X-ray diffraction, and ion conductivityof the solid electrolyte material of Comparative Example 1 were measuredas in Example 1. The measurement results are shown in Tables 1 and 2.FIG. 2 is a graph showing an X-ray diffraction pattern of the solidelectrolyte material of Comparative Example 1.

The mass proportion of O to the entire solid electrolyte material ofComparative Example 1 was 1.87%.

A battery of Comparative Example 1 was obtained as in Example 1 usingthe solid electrolyte material of Comparative Example 1.

A charge and discharge test was implemented as in Example 1 using thebattery of Comparative Example 1. The initial discharge capacity of thebattery of Comparative Example 1 was 1 μAh or less. That is, the batteryof Comparative Example 1 was neither charged nor discharged. FIG. 5 is agraph showing the initial discharge characteristics of the battery ofComparative Example 1.

TABLE 1 O/(Y + Gd) Ion Element ratio (molar ratio) molar ratio inconductivity Li Ca Y Gd Br Cl O surface region (S/cm) Example 1 2.880.07 0.50 0.50 1.70 3.97 0.08 2.08 1.2 × 10⁻³ Example 2 2.87 0.07 0.500.50 1.65 3.88 0.09 2.47 6.7 × 10⁻⁴ Example 3 2.88 0.08 0.50 0.50 1.333.26 0.20 2.68 1.0 × 10⁻⁴ Example 4 2.84 0.07 0.50 0.50 1.03 2.69 0.422.38 1.2 × 10⁻⁵ Comparative 2.86 0.07 0.50 0.50 1.03 2.69 0.43 2.75 9.0× 10⁻⁶ Example 1

TABLE 2 X-ray diffraction peak angle (2θ) Example 1 15.42° 16.80° 22.86°27.70° 28.72° — 30.54° 32.74° — — 39.76° 47.50° — Example 2 15.58°16.93° 23.01° 27.96° 28.84° — 30.70° 32.91° — — 39.88° 47.63° — Example3 15.41° 16.80° 22.87° 27.65° 28.58° 29.48° 30.52° 32.66° 33.49° 34.25°39.75° 47.61° — Example 4 15.28° 16.70° 22.77° — — 29.52° 30.45° 32.60°33.44° 34.30° — — 49.25° Comparative 15.39° 16.77° 22.83° — — 29.57°30.45° 32.67° 33.41° 34.33° — — 49.33° Example 1

Consideration

As obvious from Table 1, the solid electrolyte materials of Examples 1to 4 each have a high ion conductivity of 1×10⁻⁵ S/cm or more at aroundroom temperature.

As obvious from Examples 1 to 4, when the molar ratio of O to the sum ofY and Gd is greater than 0 and 0.42 or less, the solid electrolytematerial has a high ion conductivity of 1×10⁻⁵ S/cm or more. As obviousby comparing Examples 1 to 3 with Example 4, when the molar ratio isgreater than 0 and 0.20 or less, the solid electrolyte material has ahigher ion conductivity of 1×10⁻⁴ S/cm or more. When the molar ratio isgreater than 0 and 0.08 or less, the solid electrolyte material has ahigher ion conductivity of 1×10⁻³ S/cm or more.

As obvious from Examples 1 to 4, the molar ratio of O to the sum of Yand Gd in the surface region of the solid electrolyte material is fiveor more times the molar ratio of O to the sum of Y and Gd in the entiresolid electrolyte material.

As obvious from the X-ray diffraction patterns shown in FIG. 2 and fromTable 2, the crystal structure of a solid electrolyte material changesdepending on the content of O.

As obvious from Table 1, the contents of Br and Cl decrease with anincrease in the content of O. This may be caused by that O wassubstituted with Br and Cl during the second heat treatment in theproduction of a solid electrolyte material. That is, it is inferred thatO bound to a metal atom in the solid electrolyte material and wasincorporated into the crystal structure.

The batteries of Examples 1 to 4 were charged and discharged at 25° C.

Since the solid electrolyte materials of Examples 1 to 4 do not containsulfur, hydrogen sulfide does not occur.

As described above, the solid electrolyte material of the presentdisclosure has a high lithium ion conductivity and is suitable forproviding a battery that can be well charged and discharged.

The solid electrolyte material of the present disclosure is used in, forexample, an all solid lithium ion secondary battery.

What is claimed is:
 1. A solid electrolyte material consistingessentially of Li, Ca, Y, Gd, X, and O, wherein X is at least oneselected from the group consisting of F, Cl, Br, and I; a molar ratio ofO to the sum of Y and Gd in the entire solid electrolyte material isgreater than 0 and 0.42 or less; and a molar ratio of O to the sum of Yand Gd in a surface region of the solid electrolyte material is higherthan a molar ratio of O to the sum of Y and Gd in the entire solidelectrolyte material.
 2. The solid electrolyte material according toclaim 1, wherein X is Cl and Br.
 3. The solid electrolyte materialaccording to claim 1, further comprising: at least one selected from thegroup consisting of Sr, Ba, Al, Sc, Ga, Bi, La, Zr, Hf, Ta, and Nb. 4.The solid electrolyte material according to claim 1, wherein an X-raydiffraction pattern obtained by X-ray diffraction measurement usingCu-Kα rays includes peaks in diffraction angle 2θ ranges of 14.9° ormore and 16.1° or less, 16.2° or more and 17.5° or less, 22.3° or moreand 23.6° or less, 29.9° or more and 31.2° or less, and 32.10 or moreand 33.5° or less.
 5. The solid electrolyte material according to claim1, wherein following four mathematical expressions are satisfied:2.5≤x≤3.2;0.06≤y≤0.08;0.9≤z≤1.9; and2.4≤w≤4.4, wherein x represents a molar ratio of Li to the sum of Y andGd; y represents a molar ratio of Ca to the sum of Y and Gd; zrepresents a molar ratio of Br to the sum of Y and Gd; and w representsa molar ratio of Cl to the sum of Y and Gd.
 6. A battery comprising: apositive electrode; a negative electrode; and an electrolyte layerdisposed between the positive electrode and the negative electrode,wherein at least one selected from the group consisting of the positiveelectrode, the negative electrode, and the electrolyte layer containsthe solid electrolyte material according to claim 1.